I believe that the Nine are the nine Iron Wolves that are spoken of in the grimoire. Rumored to be suuuuuper powerful gaurdians that rose to protect the city when noone else could. Xur says he is the Nines trashman which leads me to believe that exotics are their trash (which would give weight to the fact that they are extremely powerful). What if to the Nine exotics were like common engrams? Full exotic to the Nine is like full common for the rest of us. Garbage.